The present invention relates to the field of sensing vehicles, and, more particularly, to structures used underneath roads to sense vehicles traveling on such roads, and to methods of maintaining those structures.
Methods and devices for detecting the presence of vehicles on a street or road are well known. Detecting the presence of a vehicle is done for a variety of reasons. Vehicles may be detected to monitor the traffic flow and determine road usage. This information may be utilized for transportation planning and traffic light control. Pairs of the sensing devices spaced apart along the roadway may also be utilized to monitor vehicle speeds.
Prior art vehicle detection devices include U.S. Pat. No. 3,984,764, U.S. Pat. No. 3,943,399, U.S. Pat. No. 4,449,115, and U.S. Pat. No. 5,491,475, all of which, if installed after the roadway is in place, require cutting into the pavement. Such cutting into the pavement has numerous downsides, further explained in U.S. Pat. No. 5,850,192 at Column 1, lines 18-57, which lines are incorporated herein by reference. The system of U.S. Pat. No. 5,850,192 includes attachable sections placed into an under-roadway conduit. The preferred sections are substantially rounded to be self-centering and may be weighted to maintain the probes in a substantially vertically oriented position. The original commercial implementation of the system of U.S. Pat. No. 5,850,192 included a clip attached to a carrier from above using blind rivets and washers.
However, the system of U.S. Pat. No. 5,850,192 left several shortcomings. The system of U.S. Pat. No. 5,850,192 is difficult to assemble due to inherent design constraints. For instance, installers can attach adjacent carriers of the original system together without creating a secure positive mechanical lock, and the connected carriers can become inadvertently detached during installation. If an installer does accomplish a positive attachment of adjacent carriers, then disassembly for maintenance and repair can be quite difficult. The system of U.S. Pat. No. 5,850,192 is expensive to manufacture. In particular, secondary operations in the original carrier design cannot be completed inline, but rather must be performed separately to the individual carrier units. Secondary operations include punching holes and slots into the carrier for the carrier clip, sensor, and the mating tongue piece of another carrier clip. Performing the secondary operations separately and offline decreases production efficiency, decreases accuracy between features, and increases costs. The present invention particularly improves upon the system disclosed in U.S. Pat. No. 5,850,192, as well as other problems associated with underground vehicle sensing systems.